The aftermarket is starting to look at the 4200 to make parts for (finally).
Kooks pre-install base line dyno testing
I would rather put the 200-300 buck header money on something else as the stock exhaust manifold is a good as you can find on a Base engine, maybe better than the 4bbl Pontiac OHC. Unless you really dig the "split manifold" sound. I do -- that makes it a tough call! Is it my dialup or is there no rpm reference or torque numbers? Arn't there some trailblazer headers already out there, or is it just for the 5 cylinder pickups, seems like Jrs or something like that. Fives also have a nice stock manifold.
Header results are posted on pg 10&11
What I'm impressed with is the additional torque output. Almost an extra 16 ft. lbs with a stock tune and 19 with an updated tune. Of course 10 and 15 extra ponies is good too. Not bad on a Chassis dyno. That was on a stock 04! Just think what an 06-09 would do. Not to mention what some port work would add.
Cool.